As a graphic language form for recording geographical information, electronic maps provide great convenience when one travels. However, the traditional map products are all two-dimensional, and have limitations in practical application. For example, on the actual road, there exist complex road sections such as overpasses, deep grooved sections, tunnels and so on. Those complex road sections criss-cross in space, which is difficult to be presented by two-dimensional maps. In addition, the expression form of two-dimensional maps is not intuitive, leading to difficulties in understanding.
As computer graphics, three-dimensional simulation technologies, virtual reality technologies and network communication technologies develop rapidly, the traditional two-dimensional electronic maps are revived. As a result, Internet based three-dimensional electronic maps are becoming important trend in developing the electronic maps. Three-dimensional electronic maps provide users with map functions such as map query, trip navigation by intuitively simulating real geographies. In addition, more interactions and colourful rendering techniques can be realised using the three-dimensional maps, providing more imagination room for more relevant products.
The methods for establishing three-dimensional road models in the existing three-dimensional maps may be divided into two approaches: namely an artificial modeling approach, and an automatic modeling approach. The artificial modeling approach refers to manually plotting three-dimensional road models using a three-dimensional drawing software with reference to satellite or aerial images. Clearly, this modelling approach is not highly efficient. The automatic modeling approach refers to scanning areas to be modeled using aircraft-mounted or car-mounted professional sampling devices such as cameras or radars, and automatically modelling the scanned data. Although the automatic modeling approach have an improved efficiency, the cameras and the radars are expensive. In addition, the cost of performing such scanning is high. Therefore, the cost of the automatic modeling approach concerns a majority of the electronic map developers.